U.S. Pat. No. 6,605,775 to Seeber et al. issued Aug. 12, 2003 with the title “Floating radio frequency trap for shield currents” and is incorporated herein by reference. In U.S. Pat. No. 6,605,775, Seeber et al. describe a floating shield current trap that provides first and second concentric tubular conductors electrically connected to provide a resonance-induced high impedance of current flow in a path consisting of the inner and outer conductors and their junctions thereby suppressing coupled current flow on a shield of a conductor contained within the first inner tubular conductor.
U.S. Pat. No. 6,664,465 to Seeber issued Dec. 16, 2003 with the title “Tuning system for floating radio frequency trap” and is incorporated herein by reference. In U.S. Pat. No. 6,664,465, Seeber describes a floating shield current trap provides two resonance loops formed of split concentric tubular conductors joined radially at their axial ends. Adjustment of the separation of these loops provides a change in coupling between the loops effecting a simplified tuning of the resonance of the trap for different expected frequencies of interfering shield current.
U.S. Pat. No. 6,593,744 to Burl et al. issued Jul. 15, 2003 with the title “Multi-channel RF cable trap for magnetic resonance apparatus” and is incorporated herein by reference. In U.S. Pat. No. 6,593,744, Burl et al. describe a multi-channel RF cable trap that blocks stray RF current from flowing on shield conductors of coaxial RF cables of a magnetic resonance apparatus. An inductor is formed by a curved semi-rigid trough constructed of an insulating material coated with an electrically conducting layer. Preferably, the inductor and the cable follow an “S”-shaped path to facilitate good electromagnetic coupling. The RF cables are laid in the trough and the shield conductors inductively couple with the inductor. A capacitor and optional trim capacitor are connected across the trough of the inductor to form a resonant LC circuit tuned to the resonance frequency. The LC circuit inductively couples with the shield conductors to present a signal-attenuating high impedance at the resonance frequency. The resonant circuit is preferably contained in an RF-shielding box with removable lid.
Low-power circuits can use varactors (electrically variable capacitors), field-effect transistors (used as variable gain elements or variable resistors) and like components that are directly electrically-adjustable, for use in adjusting frequency, impedance or other circuit characteristics and parameters, however such components are often unsuitable or inoperative in high fields.
U.S. Pat. No. 6,495,069 issued Dec. 17, 2002 to Lussey et al. with the title “Polymer composition” and is incorporated herein by reference. In U.S. Pat. No. 6,495,069, Lussey et al. describe a polymer composition comprises at least one substantially non-conductive polymer and at least one electrically conductive filler and in the form of granules. Their elastomer material was proposed for devices for controlling or switching electric current, to avoid or limit disadvantages such as the generation of transients and sparks which are associated with the actuation of conventional mechanical switches. They described an electrical conductor composite providing conduction when subjected to mechanical stress or electrostatic charge but electrically insulating when quiescent comprising a granular composition each granule of which comprises at least one substantially non-conductive polymer and at least one electrically conductive filler and is electrically insulating when quiescent but conductive when subjected to mechanical stress. They did not propose a means for electrically activating such switches.
U.S. Pat. No. 8,299,681 to Snyder, Vaughan and Lemaire issued Oct. 30, 2012 with the title “Remotely adjustable reactive and resistive electrical elements and method” and is incorporated herein by reference. In U.S. Pat. No. 8,299,681, Snyder et al. describe an apparatus and method that includes providing a variable-parameter electrical component in a high-field environment and based on an electrical signal, automatically moving a movable portion of the electrical component in relation to another portion of the electrical component to vary at least one of its parameters. In some embodiments, the moving uses a mechanical movement device (e.g., a linear positioner, rotary motor, or pump). In some embodiments of the method, the electrical component has a variable inductance, capacitance, and/or resistance. Some embodiments include using a computer that controls the moving of the movable portion of the electrical component in order to vary an electrical parameter of the electrical component. Some embodiments include using a feedback signal to provide feedback control in order to adjust and/or maintain the electrical parameter. Some embodiments include a non-magnetic positioner connected to an electrical component configured to have its RLC parameters varied by the positioner.
U.S. Pat. No. 8,674,695 issued Mar. 18, 2014 to Wiggins with the title “Radio Frequency Coil Arrangement for High Field Magnetic Resonance Imaging with Optimized Transmit and Receive Efficiency for a Specified Region of Interest, and Related System and Method,” and is incorporated herein by reference. In U.S. Pat. No. 8,674,695, Wiggins describes exemplary embodiments of a coil arrangement that can include, e.g., a plurality of elements which can be provided at an angle from one another. The angle can be selected to effectuate an imaging of a target region of interest at least one of a predetermined depth or range of depths, for example. In certain exemplary embodiments, the angle can be selected to effectuate an exemplary predetermined transmit efficiency for at least one of the elements. Additionally, the exemplary angle can be selected to effectuate a predetermined receive sensitivity for at least one of the elements. Further, according to certain exemplary embodiments of a coil arrangement in according to the present disclosure, the angle can be adjusted manually and/or automatically.
A journal article, “96-Channel Receive-Only Head Coil for 3 Tesla: Design Optimization and Evaluation” by Graham C. Wiggins et al. (Magn. Reson. Med. 2009 September; 62(3): 754-762. doi:10.1002/mrm.22028) describes a receive coil, and is incorporated herein by reference.
U.S. Pat. No. 4,885,539 to Roemer et al. issued Dec. 5, 1989 with the title “Volume NMR coil for optimum signal-to-noise ratio” and is incorporated herein by reference. In U.S. Pat. No. 4,885,539, Roemer et al. describe an RF volume coil with optimized signal-to-noise ratio, for NMR use, has a reduced length Lc, which is between about 0.3rs and about 1.5rs, where rs is the radius of a sample-to-be-investigated, contained within the cylindrical volume coil, with the volume coil radius rc being between about 1.0rs and about 1.6rs the “short” volume coil has an improved SNR for a voxel located substantially on the central plane of the coil, relative to the SNR of a “normal”-length volume coil with Lc greater or equal to 4rs.
A journal article, “The NMR Phased Array” by P. B. Roemer et al. (Magn Reson Med. 1990 November; Vol. 16 Issue 262 pages 192-225), describes a phased array receive coil, and is incorporated herein by reference. Roemer et al. describe ways to overlap coil loops (circular loops overlapped by spacing the centers of the circular loops at 0.75 diameter, and square loops by about 0.9 diameter; and the loops are all the same size) to reduce mutual-induction interference.
U.S. Pat. No. 6,534,983 to Boskamp et al. issued Mar. 18, 2003 with the title “Multi-channel phased array coils having minimum mutual inductance for magnetic resonance systems” and is incorporated herein by reference. In U.S. Pat. No. 6,534,983, Boskamp et al. describe a multi-channel phased array coil for use in a magnetic resonance (MR) system is disclosed herein. The phased array coil includes N coils configured in an array, each of the N coils having a geometric shape and overlapping with (N−1) coils to form an overlap area within the array. The geometric shape of each of the coils and the overlap area are configured to cause a mutual inductance between every pair of the coils to be less than 10 percent of the self-inductance of each of the N coils. At least four coils are provided in the phased array coil.
U.S. Pat. No. 6,538,441 issued to Watkins et al. on Mar. 25, 2003 with the title “RF coil for reduced electric field exposure for use in very high field magnetic resonance imaging” and is incorporated herein by reference. In U.S. Pat. No. 6,538,441, Watkins et al. describe an RF coil assembly for a very high field Magnetic Resonance Imaging (MRI) system is provided. The RF coil assembly comprises a plurality of conductors arranged cylindrically and disposed about a patient bore tube of the MRI system. Each of the conductors is configured for the RF coil assembly to resonate at substantially high frequencies. Further, the RF coil assembly comprises a plurality of capacitive elements disposed between and connecting respective ends of the conductors and further disposed in a spaced-apart relationship with the patient bore tube. The capacitive elements are for electrically interconnecting the plurality of conductors at the respective ends of the conductors.
U.S. Pat. No. 6,822,448 issued to Watkins et al. on Nov. 23, 2004 with the title “RF coil for very high field magnetic resonance” and is incorporated herein by reference. In U.S. Pat. No. 6,822,448, Watkins et al. describe an RF coil assembly for a very high field Magnetic Resonance Imaging (MRI) system is provided comprising a plurality of conductors arranged cylindrically and disposed about a cylindrical patient bore tube of the MRI system and a plurality of capacitive elements for electrically interconnecting the plurality of conductors at respective ends of the conductors. The conductors have a width selected for the RF coil assembly to resonate at substantially high frequencies. A very high field Magnetic Resonance Imaging (MRI) system is provided that comprises a RF coil assembly adapted to resonate at substantially high frequencies, a RF coil shield assembly and a plurality of RF drive power cables.
There is a long-felt need for improved SNR from received signals in an MRI system.